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The brain’s social network

Neuroscientists often attempt to attribute various behaviors and traits to certain regions of the brain. These findings make for neat science and great headlines, and while some of these results are little better than phrenology claims, many are highly reliable. The good ones are confirmed and replicated by multiple labs and substantiated using a variety of different methods, such as lesioning or animal and human imaging models. For example, we know with relative certainty that much of the occipital lobe is in charge of processing visual information and that the hippocampus is heavily involved in transitioning from short-term to long-term memory. However, there is much in our behavior and our brains that we still do not understand, and it is highly tempting to simply assign certain sections of the brain to different traits when in fact the underlying mechanisms are much more complicated. This tendency has become increasingly easy in the past decade with the rise of functional neuroimaging studies, where a region of the brain is seen to “light up” with activity when performing certain types of tasks. Voxel-based morphometry (VBM) studies take these investigations a step further, looking at how gray matter volume in our brains correlates to different traits and behaviors. Two recent examples of VBM studies have investigated the neural correlates of social networking and extroversion, finding connections between amygdala size (among other regions) and social tendencies.

The first study, out of University College London and published in the Proceedings of the Royal Society Biological Sciences, found that people with more Facebook friends had increased gray matter volume in certain regions of the brain associated with social interactions. The authors of the study hypothesized that the number of one’s online friends could predict the relative brain size of regions important for social networking, particularly those involved in social cognition and mentalizing (the ability to recognize social cues and take another’s perspective). These areas include the fronto-parietal cortical circuit, medial prefrontal cortex, and amygdala. However, these frontal cortical regions were not identified in the study, and instead the researchers discovered greater volume in the left middle temporal gyrus, right entorhinal cortex, and right posterior superior temporal sulcus, as well as the amygdala to a lesser extent. These areas are implicated in social cognition, perception of movement and intention (both physical and social), and autobiographical and associative memory. Based on these findings, the authors speculate that individuals with greater brain volume in these regions are more adept at the skills needed to maintain online socio-personal connections, such as enhanced memory of face-name combinations and awareness of movement of individuals in social circles. However, of these regions only the amygdala was correlated with real life social interactions, and none of the other originally proposed areas were found to correlate with social network size.

The second study, published this week in PLoS ONE, also reports that individuals who are more extroverted show increased volume in the amygdala, as well as in the orbitofrontal cortex (OFC). Researchers from the Netherlands administered the NEO Five Factor personality assessment to 65 individuals to subjectively measure extroversion and neuroticism levels. They also had participants undergo an MRI scan and used VBM analysis to measure the size of certain pre-determined regions of the brain against extroversion scores, including the amygdala, anterior cingulate cortex, and OFC. Controlling for age, sex, and total gray matter volume, researchers discovered that individuals who scored higher on the extroversion scale had significantly larger amygdala and orbitofrontal cortices, as well as finding a significant correlation between total gray matter volume and extroversion scores.

As stated above, the amygdala is one of the brain’s emotional centers and is important in social interactions, both online and offline. It is crucially implicated in recognizing and processing positive and negative emotions, both in oneself and from the facial expressions of others. The OFC is also commonly associated with emotion regulation, as well as reward valuation and decision-making, mainly through its connections to limbic structures such as the amygdala, striatum, and hypothalamus. However, it is not typically linked to social interactions, and the authors speculate that their findings are evidence of the amygdala and OFC’s involvement in a greater sensitivity to positive experiences and social interactions, rather than interpersonal skills themselves.

While the findings from these two studies are intriguing and compliment one another nicely, caution must be taken in the interpretation placed on these results. Correlation analyses state only an association, not a causation, and, as recently brilliantly exhibited by Business Week, these connections can be highly questionable at times. This is particularly true of imaging studies, where investigators can go fishing for regions to attribute their target behaviors to. Interpretations of correlations are quick to come by, and rationales for connections in unexpected areas of the brain can be justified all too easily when a publication is on the line. A priori regions of interest are thus crucially important, providing groundings for current explorations based on previous studies and alternative research methods. I am in no way denouncing VBM studies and their value and viability generally, or these studies in particular, however, I do caution against the interpretations that can be carelessly made with them. Additionally, in studies like these, it is unknown whether the size of the regions predicts the behavior or if the brain adapts and grows to incorporate new connections based on the repetition and reinforcement of certain actions. In regards to the studies at hand, their confirmation of the amygdala’s role in social interactions is highly supported, however, it is unknown whether the increase in brain size is a predictor of social ability and network size, or whether practice of interpersonal skills helps to foster neurogenesis in these regions.